The invention relates generally to methods and compositions for treating and preventing multiple sclerosis, and more particularly to methods and compositions for treating and preventing multiple sclerosis by administration of synthetic calcitonin, calcitonin-like peptides or calcitonin mimetics to a patient.
Multiple Sclerosis
In multiple sclerosis (MS), inflammation of nervous tissue causes loss of myelin, a fatty material that acts as a protective insulation for nerve fibers in the brain and the spinal cord. This loss of myelin, or demyelination, leaves multiple areas of scar tissue, or sclerosis, along nerve cells. Consequently, the sclerosis results in multiple and varied neurological signs and symptoms, usually with repeated relapse and remission.
To date, treatment of MS has focused on the reduction of symptoms, which includes, but are not limited to, reduced or loss of vision, stumbling and uneven gait, slurred speech, as well as urinary frequency and incontinence. In addition, MS can cause mood changes and depression, muscle spasms and severe paralysis. The cause of MS is unknown, but an immunologic abnormality is suspected in causing the initial inflammation, with few clues presently indicating a specific mechanism (The Merck Manual, 16th Edition, 1993 Merck & Co.).
MS is more frequent at northern latitudes. Depending on the region in the Western world, the prevalence varies with 50-150 cases per 100,000 individuals. In the United States alone, some 250,000-350,000 individuals have an MS diagnosis. Females are twice as likely to develop MS when compared to males.
Current treatments for MS generally suppress the immune system. For example, one treatment includes transplantation of bone marrow along with administration of cytostatics and immunosupressive drugs. This treatment works for some patients, but it is expensive and includes several risks for patients. Additionally, the administration of cytostatics is considered controversial in treating MS because its effects are unclear and potential side-effects are severe.
Other treatments aim to cure or delay the MS disease. Among certain patients, interferon-beta (AVONEX™ and BETASERON™) reduces the symptoms of MS and is therefore administered to most patients for ethical reasons. Unfortunately, the mechanism of action of interferon-beta is unclear for these patients. Like suppressive treatments, interferon-beta is expensive. For other patients, glatiramer acetate (COPAXONE™) reduces the frequency of attacks; however, its side effects are substantial and problems occur in distinguishing the symptoms of MS from the side effects of glatiramer acetate.
The latest drug to be approved by the FDA for treatment for relapsing forms of MS is TYSABRI™ (NATALIZUMAB, formerly known as ANTEGREN). As noted above, most drugs for treating MS suppress the immune system. TYSABRI™, however, blocks immune cells from crossing into the central nervous system (CNS), thereby preventing damage to the nerves. One drawback of TYSABRI™ is its side effects, which include headache, fatigue, urinary tract infection, depression, lower respiratory tract infection, joint pain and abdominal discomfort. Another drawback with TYSABRI™ is that no long-term safety information is available.
Currently, an effective treatment for MS does not exist. Treatment is focused on merely reducing its symptoms. Tests with transplantation and different drug treatments to cure the disease have not demonstrated any solutions. Accordingly, a demand for drugs that can protect an MS patients from the severe development of the disease is therefore of high priority.
Calcitonin
In many instances, 1,25(OH)2D3 only completely prevents EAE at doses that are likely to cause hypercalcemia, which leads to increased circulating levels of calcitonin. Furthermore, hypercalcemia independent of 1,25(OH)2D3 can prevent EAE in female mice. Calcitonin has been shown to have anti-inflammatory properties in several animal models of inflammatory disease. Finally, calcitonin has also shown promise in treating the autoimmune disease rheumatoid arthritis.
Calcitonin is a thirty-two amino acid polypeptide hormone that participates in calcium and phosphorous metabolism. It is cleaved from a larger prohormone (approximately 15 kDa) and decreases serum calcium by inhibiting the reabsorption of calcium from bone and kidney. Calcitonin is synthesized in the parafollicular or C-cells in the thyroid gland in mammals, but it is also isolated from the ultimobrachial glands in birds, fish and amphibians.
A large number of diseases are associated with abnormally increased or decreased levels of calcitonin; however, pathologic effects of abnormal calcitonin secretion per se are not generally recognized. As such, calcitonin has several therapeutic uses. For one, it is used to treat hypercalcemia resulting from a number of causes. Additionally, calcitonin is a valuable therapy for Paget disease, which is a disorder in bone remodeling. Furthermore, it is a valuable aid in the management of certain types of osteoporosis.
Calcitonin has been obtained from several different species, including, but not limited to, bovine, eel, human, porcine, rat and salmon. In all of these species, the primary structure of calcitonin is similar, although some structural variations exist (see Table I). Of the thirty-two amino acids present in calcitonin, eight residues are conserved across all species. Additionally, calcitonins with amino acid sequences identical to the natural forms have been produced by chemical synthesis, as well as by recombinant technology.
TABLE IAmino Acid Sequences of Calcitonin inRepresentative Species.SpeciesAmino Acid SequenceBovineCys-Ser-Asn-Leu-Ser-Thr-Cys-Val-Leu-Ser-Ala-Tyr-Trp-Lys-Asp-Leu-Asn-Asn-Tyr-His-Arg-Phe-Ser-Gly-Met-Gly-Phe-Gly-Pro-Glu-Thr-Pro(SEQ ID NO: 1) EelCys-Ser-Asn-Leu-Ser-Thr-Cys-Val-Leu-Gly-Lys-Leu-Ser-Gln-Glu-Leu-His-Lys-Leu-Gln-Thr-Tyr-Pro-Arg-Thr-Asp-Val-Gly-Ala-Gly-Thr-Pro(SEQ ID NO: 2) HumanCys-Gly-Asn-Leu-Ser-Thr-Cys-Met-Leu-Gly-Thr-Tyr-Thr-Gln-Asp-Phe-Asn-Lys-Phe-His-Thr-Phe-Pro-Gln-Thr-Ala-Ile-Gly-Val-Gly-Ala-Pro(SEQ ID NO: 3) PorcineCys-Ser-Asn-Leu-Ser-Thr-Cys-Val-Leu-Ser-Ala-Tyr-Trp-Arg-Asn-Leu-Asn-Asn-Phe-His-Arg-Phe-Ser-Gly-Met-Gly-Phe-Gly-Pro-Glu-Thr-Pro(SEQ ID NO: 4) RatCys-Gly-Asn-Leu-Ser-Thr-Cys-Met-Leu-Gly-Thr-Tyr-Thr-Gln-Asp-Leu-Asn-Lys-Phe-His-Thr-Phe-Pro-Gln-Thr-Ser-Ile-Gly-Val-Gly-Ala-Pro(SEQ ID NO: 5) SalmonCys-Ser-Asn-Leu-Ser-Thr-Cys-Val-Leu-Gly-Lys-Leu-Ser-Gln-Glu-Leu-His-Lys-Leu-Gln-Thr-Tyr-Pro-Arg-Thr-Asn-Thr-Gly-Ser-Gly-Thr-Pro(SEQ ID NO: 6)
Calcitonin has several important structural features. Salmon calcitonin, for example, has a disulphide bridge (cystine link) between the first and seventh amino acids at the amino end of the polypeptide chain. This disulphide bridge is essential for its biological activity as it causes the amino terminus to assume the shape of a ring. Additionally, salmon calcitonin has a prolinamide group at the carboxyl terminal amino acid. Alternative splicing of the calcitonin pre-mRNA can yield a mRNA encoding calcitonin gene-related peptide; this peptide appears to function in the nervous and vascular systems.
Interestingly, salmon calcitonin has been shown to be considerably more effective in arresting bone resorption than human forms of calcitonin. Several hypotheses have been offered to explain this observation and include the following: (1) salmon calcitonin is more resistant to degradation; (2) salmon calcitonin has a lower metabolic clearance rate (MCR); and (3) salmon calcitonin may have a slightly different conformation, resulting in a higher affinity for bone receptor sites.
Despite the advantages associated with the use of salmon calcitonin in humans, there are also disadvantages such as cost and limited method of administration (by injection). Additionally, resistance to calcitonin therapy may occur with long-term use. Furthermore, some patients develop antibodies to non-human calcitonin, calcitonin mimetics would be useful for such patients. Therefore, use of synthetic calcitonin, calcitonin-like peptides or calcitonin mimetics, either in place of native calcitonins or in rotation with native calcitonins, may help to avoid resistance to such treatment during long-term use.
Needed in the art of multiple sclerosis treatment is a method of effectively using calcitonin, possibly in combination with other multiple sclerosis treatments, as an effective therapeutic.